Simulation Software Design And Simulative Investigations For Nonlinear Imaging Of Multiple Scatterers

When intense laser beams modulated by small scale scatterers pass throughnonlinear medium, light spot will generate at somewhere downstream with scatterershape and higher light intensity than that of background, which is the nonlinearimaging effect. Such hot image can bring great damage to the safe running of lasersystem even under safe damage thresholds, and seriously threatens the safe running ofhigh power laser system and limits the performance improvement of high power lasersystem. In the research on high power laser system manufacturing and laser nonlinearpropagation, computer numerical simulation has become one of the main methods. Itcan be used to reproduce and predict some important nonlinear propagationphenomena and help people to discover certain related nonlinear propagationcharacteristics with low cost. It has played an important role in the research of hotimage effect, and some fundamental laws of hot image effect for the single scatterermodulation case and the formation of hot images in the intensity-typed doublescatterers has been discovered through it.A computer numerical simulation software which can be used to systematicallysimulate the nonlinear propagation of the hot image formation for multiplephase-typed scatterers has been designed in this thesis. Based on this software, the hotimage effect in the case of phase-typed double scatterers is investigated, and relatedbasic laws are obtained. The main works are as follows:First, a computer numerical simulation software is designed and developed forsimulating the nonlinear propagation of the hot image formation for multiplephase-typed scatterers. Based one the symmetrical split-step fast fourier transformalgorithm, this software can simulate the nonlinear propagation of laser beam in astraight optical path including wirelike scatterers, free spaces, Kerr nonlinear mediumslabs. Moreover, it also has the functions for designing optical path and visualizingsimulation results. Besides, some useful functions are designed, such as obtaining thedistribution data of the complex amplitude of the optical field like a CCD camera anddirectly visualizing it. To improve the efficiency of qualitative analysis, a onedimensional sample case of beam is considered to reduce the data in simulation.Second, the hot image effect for the phase-typed double scatterers case isinvestigated simulatively. At first, some basic problems, such as whether there will behot image or not, the fringe number in the hot image plane, the on-axis propagation distance of the hot image plane etc., are studied. It is found that there are two hotimage fringes in the conjugate plane and the in-beam positions of them are identical tothose of the scatterers.In addition, the phase modulation depth caused by scatterers and the distancebetween two scatterer are two fundamental factors in this case. Their influence on themaximum intensity in the hot image plane is investigated. It is found that they arevery important factors in hot image effect because their variation can lead to largefluctuation in the hot image intensity.